1. Field of the Invention
The present invention relates generally to, the field of optical guides. More specifically, the present invention relates to the method and apparatus of confining a non-atomic particle in a laser beam and guiding the particle confined in the laser beam through a hollow core optical fiber.
2. Background Art
Radiation pressure based transportation of atomic sized particles has been used to achieve high precision non-mechanical manipulation of such particles. An atom placed in an optical beam is attracted to or repelled from regions of high intensity, depending on the polarizability of the atom at the optical frequency. In particular, laser guidance of non-atomic particles utilizes optical forces arising from the deflection and scattering of light, which forces enable the confinement of a particle inside a laser beam and then manipulate the confined particle in a desired way. The existence of such optical forces was used in a number of optical traps. For example, optical tweezers allow dielectric particles to be trapped near the focus of a tightly focused high power laser beam and are used to manipulate biological particles, such as viruses and bacteria, microorganisms, blood and plant cells, and chromosomes. Optical tweezers allow a user to manipulate small particles in aqueous medium, but they do not allow the user to perform the same manipulation in the air. Optical traps for atoms are used in investigations of ultra cold collisions and collective effects of trapped atoms.
Most known techniques for trapping atoms in a tightly focused laser beam and transporting atoms together with the laser beam have limitations in that the trapping occurs only in a small region near the focal point of the laser. As a result, imaging and detecting devices utilizing optical traps must be built around a sample chamber, which often limits the size of the chamber in the devices. Since trapping and transporting particles occurs inside the chamber, then such imaging and detection devices require that the laser beam be steered from outside the chamber. Moreover, optical trapping forces are typically not large enough to trap particles in the laser beam, if the background medium in the chamber is turbulent or convective. Furthermore, in the optical tweezers method and device only a substantially transparent particle possesses such optical qualities that the axial force exerted on the particle in a laser beam can trap the particle inside the beam.
To improve the ways to manipulate particles through various media over longer distances, and to transport cold atoms from one vacuum system to another, the technique of guiding atoms through a hollow core optical fiber was devised. Fiber-guided atoms are deflected from the inner surface of the fiber by light that is also guided in the fiber. Optical forces induced by the laser light guided in a fiber may be used to reflect atoms from the inner wall of a hollow core optical fiber. In such a setting, laser light is coupled to the lowest-order grazing incidence mode and the laser frequency is tuned to the red side, so that atoms are attracted to the high intensity region at the center of the fiber. Atoms guided in a fiber this way undergo a series of lossless oscillations in the transverse plane and unconstrained motion in the axial direction.
While the method of guiding atoms through optical fibers was a step forward in developing means for manipulating and transporting particles from a source to a desired destination, an inherent limitation of such a method was the atomic size of a manipulated particle. Because of the atomic size, the wave length of the guiding laser beam had to be close to that of an atomic transition, and the manipulation itself could be performed only in a vacuum, therefore, requiring a special vacuum chamber. The transportation process of atomic particles itself is limited to transporting a few kinds of materials, essentially ruling out manipulating and guiding atoms of a broad range of materials. In nano-fabrication processes (guiding atoms and precisely depositing them on a substrate to form nanometer size features), operating with atoms does not allow achievement of high throughput, as it would be desirable in any industrially applicable technique.
The need, therefore, exists to provide a method and device for manipulating and guiding microscopic (non-atomic) particles through a suitable medium along straight and bent trajectories. It is also desirable to provide such method and device, capable of guiding particles of a wide range of materials in non-vacuum environment and depositing the particles on various kinds and shapes of substrates.
To address the above-described need and provide a solution to the enumerated problems, it is, therefore, the object of the present invention to develop a particle guide for a non-contact, non-mechanical manipulation of atoms, clusters and micron-size particles. The invention provides a method and device which use laser light to trap particles optically within the hollow region of a hollow core optical fiber and flexibly transport the particles along the fiber over long distances.
It is another object of the present invention to provide a technique for guiding a wide variety of particles, including biological and aerosol particles, along the optical fibers to desired destinations.
It is yet another object of the present invention to have a method and device for guiding particles in an ambient, aqueous or gaseous environments, including an inert gas environment, which may be desirable for fabrication purposes.
It is also an object of the present invention to deliver liquid and solid particles to a substrate by method of laser guidance in hollow core optical fibers after extracting the particles from source backgrounds, which method allows a user to fabricate micron-size surface structures, such as, for example, electrical circuits and micro-mechanical devices, on a virtually unlimited variety of substrates, including semiconductors, plastics, metals and alloys, ceramics and glasses. The particles deposited on such substrates can be metals and alloys, semiconductors, plastics, glasses, liquid chemical droplets and liquid droplets containing dissolved materials or colloidal particles.
Also an object of the present invention is to use fiber optic particle guides for non-contact, non-mechanical manipulation of microscopic particles. The particles include those, which are biological in origin, such as bacteria, viruses, genes, proteins, cells, and DNA macromolecules. The particles can also be inorganic, such as glass, polymers, and liquid droplets.
Another object of the present invention is to provide a method of controlling and manipulating non-atomic particles by trapping them within an optical fiber anywhere along the length of the fiber.
In particular, the laser guiding device comprises a laser beam source generating a laser beam, which is directed to an entrance of a hollow core optical fiber by a focusing lens. A source of the particles to be guided through the fiber provides a certain number of particles near the entrance to the fiber. The particles are then drawn into the hollow core of the fiber by the focused laser beam, propagating along a grazing incidence path inside the fiber. Laser induced optical forces generated by scattering, absorption and refraction of the laser light by a particle traps the particle close to the center of the fiber and propels it along. It will be described in more detail below that any micron-size material, including solid dielectric, semiconductor and solid particles as well as liquid solvent droplets, can be trapped in laser beams and transported along optical fibers due to the net effect of exertion of these optical forces. After traveling through the length of the fiber, the particles can be either deposited on a desired substrate or into an analytical chamber, or dealt with depending on the goal of a particular application.
In another embodiment of the present invention, the same principle of particle manipulation can be used to levitate particles inside a hollow core fiber. In such an apparatus, particles or liquid droplets captured by a tightly focused laser beam are drawn into a vertically positioned fiber. After a certain distance inside the fiber, the propelling axial optical force pulling the particle up will be balanced by the gravitational force acting on the particle. Such a balance of forces makes the particle levitate in an equilibrium position, allowing the estimation of the magnitude of the propelling force. Similarly, if a particle is trapped in a horizontally positioned optical fiber by two laser beams entering the fiber from two opposing ends of the fiber, the particle will levitate in a certain equilibrium position inside the fiber where a variation of the intensity of the lasers allows one to estimate the magnitude of the force confining the particle in the center of the fiber.
By directing particles along the fiber onto the substrate, micron-size features: of desirable shape can be fabricated by direct deposition of micron-size particles. Such features are built up by continued addition of particles, which can be fused together on the substrate by various techniques including in-flight melting of the particles, and subsequent coalescence of molten droplets on the substrate, simultaneous deposition of solid particles and liquid precursors, wherein the liquids serve to fill the gaps between solid particles, coalescence of liquid precursors on the substrate and subsequent decomposition by laser heating to form the final product on the substrate, sintering of the deposited material by laser, or chemical binding.